Question about KEF Audio Cresta 2 Speaker
Hate to admit it but I'm a musician with absolutely no knowledge of how to test a good or bad speaker, other than running a 9v battery to the terminals for + and - determinations and seeing if the speaker goes in or goes out. I have a sperry dm-350a digital multimeter...would like to test a speaker and horn to see if they work, before I buy. How do I do it? Does blk. lead plug into com and red into Ohm? What should the setting on the ohm meter be for an 8-ohm speaker? What are the parameters for an 8-ohm speaker..that is, what are the minimums and maximums that the meter should read to determine if the speaker is good or is bad. Thanks for your help. Dave
To be honest, a multimeter isn't going to tell you a whole lot more about the state of the speaker than your game with the 9V battery (although it's less likely to damage a small speaker). The main reason for this is that speakers are designed to have quite different ac and dc resistances (technically, the ac version is called "impedance" - though both are measured in ohms). The multimeter measures the (dc) resistance - which varies depending on the size and quality of the speaker, while the 8 ohm spec applies to the (ac) impedance. Remember also that a lot of the bad things that can happen to a speaker are mechanical, and won't show up on an electrical test. The only really reliable way to test a speaker is to insist on hearing music - preferably something with a broad frequency range - played through it at a range of volumes before you buy. If the vendor is reluctant to oblige, then you can probably guess what state the thing is in. (If you still want to try the ohm meter out, then one lead in "common", the other in "ohm" is a good start (doesn't make a lot of difference which goes where). With an analog meter, switch between the ohms ranges until you find one that puts the needle near the middle of the dial (remember, the ohms scale reads backwards). With a digital meter, use the lowest range that doesn't give you an error. You aren't going to damage either speaker or meter in any of the ranges.)
Posted on Jun 22, 2007
Zeusfaber partially answered your question and there is not a set measurement for measuring speaker resistance. If the speakers have a crossover network it will also affect measurements at connections. The impedance of speakers is an in use AC measurement with an applied signal. Impedance measurements requires the use of an impedance meter versus an ohm meter. Sound signals are generated from an amp in an variable AC wave form so they are measured in AC impedance. This variable AC wave form is what causes the speaker magnets to vibrate back and forth to produce sound. When using an ohm meter on a speaker it will only measure the resistance of the windings on the speaker core and these windings are of different length according to manufacture and speaker type, tweeter, woofer, midrange, wire size, magnet, etc. In short, measuring with ohm meter is not reliable and it's best to listen to with high freq and low bass freq, then inspect cones and speaker mounting for damage, movement or looseness. Physical damage to speakers cannot be measured by any meter so in use is the best test. Using a 9v dc battery on ac speakers and crossovers could cause damage also unless it is a very high wattage speaker, which most are not. Speaker signals in home and car speakers are usually in milivolts, which is a very low voltage, so be very cautious. I'm no electrical engineer but over the years this is what I've learned about speaker science and not getting burned on used speakers.
Posted on Feb 25, 2008
Posted on Apr 23, 2010
TEST IT WITH A DIGITAL MULTIMETER THE SPEAKER ITSELF NOT WITH THE CROSSOVER IT SHOULD READ AROUND 6 OHMS. SPEAKERS WILL ONLY READ ABOUT 75 PERCENT OF THERE REAL IMPEDANCE ON A MULTIMETER
Posted on Aug 01, 2014
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Posted on Jan 02, 2017
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